Various types of bearings, including rolling element bearings, are known in the art. A bearing is generally a device used to reduce friction between moving surfaces and to support moving loads. One common type of bearing is a rolling element bearing that typically includes an outer ring, inner ring, and rolling elements. The outer ring is larger in diameter than the inner ring such that a number of rolling elements, in the form of solid balls or rollers, are placed at intervals in the open space between the inner and outer rings.
Proper lubrication between these rolling elements and other relative moving parts is essential and often required in many different kinds of bearings to extend bearing life and prevent bearing failure. Generally, there are many types of lubricants. For instance, grease is one of the most well known lubricants. Grease is typically packed into a bearing so that it can fill the areas between the various moving parts, and in particular, the balls or rolling elements. Often, the useful life of a bearing depends on the proper lubrication of the bearing, and the type of lubrication that is used. This may be especially true in bearings where operating conditions may include caustic or corrosive substances, dirt, moisture, and high or low temperatures and pressures. In operation, the lubricant forms a thin film that separates the moving parts, such as separating the balls or rollers from the inner and outer ring to prevent direct metal-to-metal contact. The film is formed as a function of the speed of the rolling elements. The higher the speed of the roller element, the more heat is generated and the more the oil tends to thin or lose its viscosity. At high heat, the oil will no longer support the loads and metal surfaces will contact and wear rapidly. Previously, rolling element bearing greases were made with mineral oils, or Group I oils, as the base oil for the grease. However, the Group I mineral oils tended to thin at higher temperatures, resulting in metal to metal surface contact and rapid wear. Moreover, Group I mineral oils are limited in oxidation lifetime and lose viscosity swiftly as temperatures increase. Synthetic oils have been used as the base oil for a rolling element grease as well, to improve the effective temperature range of a rolling element bearing grease. However, synthetic oils are significantly more expensive to use.
Thus, there is a need to provide a rolling element bearing grease that provides for a greater effective temperature range than conventional Group I mineral oils, and that is less expensive than the synthetic oils.